It’s a suggestion alien to Mexico City residents who have long shunned tap water in favor of the bottled kind and to the throngs of tourists who visit the city each year, bringing with them fears of “Montezuma’s Revenge.” But a law recently approved by Mexico City’s legislators will require all restaurants to install filters so they can offer patrons free, drinkable water that won’t lead to stomach problems and other ailments.

Bad tap water accounts in part for Mexico being the world’s top consumer of bottled water and — worse — soda, some 43 gallons per person a year.

With an obesity epidemic nationwide, the city’s health department decided to back the water initiative.

Mexico City officials say 65,000 restaurants will have six months to install filters once the bill is signed later this month. Health inspectors will make periodic visits and impose $125 to $630 fines to those not complying. The law doesn’t cover thousands of food stalls along Mexico City’s streets.

Some restaurants already have filters. But when business consultant Jose Frank recently ate tacos with two colleagues at Yucatan Cravings in the Zona Rosa tourist district, they all had bottled water.

“I’m afraid to drink the water for everything they say. I don’t feel secure. I prefer bottled,” Frank said.

A general distrust of tap water is not without reason. The city’s giant 1985 earthquake burst water pipelines and sewers, increasing waterborne diseases, and officials blamed water supply systems for a spread of cholera in the 1990s.

Tourists still dread getting diarrhea from the microbes in untreated water. It’s a phenomenon so infamous, the bad water even starred in a “Sex and the City” movie, when Charlotte suffered the runny results of accidentally opening her mouth while showering in a Mexican resort.

Mexico City’s health secretary said 95 percent of the capital’s drinking water is clean, based on daily checks of chlorination at various treatment plants. But experts note that while Mexico City water leaves the plant in drinkable form, it travels through old underground pipes and dirty rooftop water tanks to the consumer.

Mexicans consume 69 gallons of bottled water per capita each year, mostly from 5-gallon jugs delivered by trucks to restaurants and homes. The number in the U.S. is 31 gallons, according to Jose Martinez-Robles, of the New York City-based consultant Beverage Marketing Corp.

It’s not cheap. The large jugs can cost more than $2 in a country where the minimum daily wage is $5. One-liter water bottles range from 50 cents to a dollar.

Giants such as French Danone, and Coca-Cola and PepsiCo are finding that bottled water is the fastest growing segment of their business.

Martinez-Robles estimates the bottled-water market in Mexico reached $5 billion in 2012, suggesting it will be hard to get Mexicans to change their habits and trust what comes out of their taps, even if it is filtered.

“It’s a huge market,” he said. “We don’t trust our water distribution system. I’d say it’s more of a cultural thing than hygiene.”

High consumption of bottled water does not translate to healthier lifestyles, though. Seven out of 10 Mexicans are overweight and the country has surpassed the U.S. in obesity rates, according to a United Nations report, mostly due to a diet of fatty foods and sugary sodas.

Legislator Jorge Gavino thought requiring restaurants to offer free water from the tap would help Mexicans downsize while saving money.

Luis Najar of Las Magaritas restaurant said installing an ultraviolet-light filter, visible to customers from behind the bar, has changed their drinking habits. More people ask for pitchers of water.

“We put it out here so everyone can see it’s filtered and pure,” he said.